The peak-end rule is a psychological heuristic in which people judge experiences largely based on how they were at their peak and at their end. This occurs regardless of valency (whether pleasant or unpleasant). According to the heuristic, other information aside from that of the peak and end of the experience is not lost, but it is not used. This includes net pleasantness or unpleasantness and how long the experience lasted. The peak–end rule thereby comprises extension neglect and duration neglect.
This heuristic was first suggested by Daniel Kahneman and others. He argues that because people seem to perceive not the sum of an experience but its average, it may be an instance of the representativeness heuristic.
The rule was so-named by Kahneman after studying the implications of a classic experiment. Participants in a laboratory study were asked to listen to a pair of very loud, unpleasant noises played through their headphones. One noise lasted for eight seconds. The other lasted sixteen. The first eight seconds of the second noise were identical to the first noise, whereas the second eight seconds, while still loud and unpleasant, were not as loud. Later, the participants were told that they would have to listen to one of the noises again, but that they could choose which one. Clearly the second noise is worse–the unpleasantness lasted twice as long. Nonetheless, the overwhelming majority of people chose the second to be repeated.
In one experiment, subjects were exposed to loud, painful noises. In a second group, subjects were exposed to the same loud, painful noises as the first group, after which were appended somewhat less painful noises. This second group rated the experience of listening to the noises as much less unpleasant than the first group, despite having been subjected to more discomfort than the first group, as they experienced the same initial duration, and then an extended duration of reduced unpleasantness.
The peak-end rule has been widely applied to business and marketing. Larina Kase, business psychologist and New York Times bestselling author, has written extensively on the applications of Peak-End rule to marketing in specific. In an article, she discusses the benefits of focusing on the peak and especially the end of customer experiences with the business, and the positive effect that the new focus will have on flow of customer referrals.
A 2006 study at the University of Canterbury in Christchurch, New Zealand was carried out, analyzing the implications of the peak-end rule on individuals after taking vacations. The study found, in part, that experiences have a limited capacity for retrospective feelings about them. The feelings that immediately fill this capacity are those felt at the end and the peak of the experience. This data supersedes many effects of the length of the vacation. That is to say, the duration of a vacation has negligible effects when compared to the overall happiness at the peak and end of the vacation itself. The results of the study could be applied to a more economical time frame for vacation-taking, as well as planning activities surrounding one large event, the "peak," and a memorable ending experience.
See also 
- Schwartz, Barry. The Paradox of Choice.
- Kase, Larina. "How to Use the Peak-End Rule in Marketing".
- Kemp, Simon; Christopher D.B. Burt, Laura Furneaux (2006). "A test of the peak-end rule with extended autobiographical events". Memory & Cognition 36 (1): 132–138.
- Kahneman, D. (1999). Objective Happiness. In Kahneman, D., Diener, E. and Schwarz, N. (eds.). Well-Being: The Foundations of Hedonic Psychology. New York: Russel Sage. pp. 3–25.
- Open-source pre-publication manuscript: Kahneman D, "Experienced utility and objective happiness: a moment-based approach", in Choices, Values and Frames, D. Kahneman and A. Tversky (eds), New York: Cambridge University Press.